Compared to placebo, nearly half the people taking the medication are non-smokers at 12 weeks.

But reports of violence and aggression with the medicine have surfaced after the drug hit the market and large numbers of people started taking it.

“Some people have reported that they’ve had abnormal dreams, nightmares, or changes in their mood, even feeling more anxious and agitated,” says Dr. Alicia Kaplan, a psychiatrist at Allegheny General Hospital.

But occasional reports aren’t enough to prove cause and effect.

Chantix enters the brain and sits in the receptors that play a role in the craving for cigarettes. Nicotine from cigarettes moves in and out of these receptors quickly, causing the craving. Chantix sits in there longer, so you don’t have those feelings.

This may also affect another brain chemical called dopamine. This can affect mood.

Some experts add that quitting smoking itself can worsen depression.

As a legal defense for violence, there is nothing medically conclusive to show that Chantix is causative. Other factors can muddy the picture like alcohol and mood problems.

It may be that people with mood issues and mental health conditions are more sensitive. The clinical trials involved people with no psychiatric problems.

“They should really take real life situations, especially since a lot of the patients that have chronic mental illness also have a higher rate of smoking,” says Dr. Kaplan. “They need to carefully look at that patient population as well.”